- Introduction to heredity
- Fertilization terminology: gametes, zygotes, haploid, diploid
- Alleles and genes
- Worked example: Punnett squares
- Mendel and his peas
- The law of segregation
- The law of independent assortment
- Probabilities in genetics
- Mendelian genetics
Pedigrees are a useful method to model the inheritance patterns of traits within families. By using symbols and analyzing phenotypes, we can infer genotypes and understand the role of autosomal dominant traits. The trait of freckles serves as a practical example here and shows the complex world of genetic inheritance patterns. Created by Sal Khan.
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- how can i identify if the trait tracked is sex-linked recessive or sex-linked dominant(12 votes)
- if all the generation has atleast one affected person then the trait tracked is dominant.
if the affected male and female individual's ratio is more or less similar then it is autosomal
for sex linked
if it is x linked then most males are affected and if the mother affected then all the sons are affected
if it is y linked then all the males are definitely
- I might just be very stupid but how did he know that the pedigree was autosomal dominant? Will it always tell you if it is or not. Additionally, how in the world did he know freckles was the dominant trait?(7 votes)
- You are not stupid and in general, autosomal traits/disorders will show up in both males and females with generally the same frequency. X linked traits/disorders are expressed in predominantly males.(10 votes)
- Could someone provide a simple definition of an allele? Thanks!(6 votes)
- One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. (from the dictionary)(9 votes)
- How can I say whether or not a trait is dominant just by seeing the pedigree?(6 votes)
- Dominant traits are always expressed in the next generation. So, if a couple with identical phenotypes couples and produces a child with a different phenotype, the two would've had to be carriers for this recessive trait.(5 votes)
- How can I say whether or not a trait is dominant just by seeing the pedigree?(4 votes)
- In the offspring of the cross, what ratios are observed? You will able to tell which traits are dominant by looking at how many of the off srping carry it and if it fits a specific pattern.
Google "pedigree charts" and you will see good layouts(4 votes)
- Why can't a dominant trait skip a generation?(3 votes)
- A dominant trait can't skip a generation because it always shows up if present. Recessive genes seem to "skip" generations simply because they're covered by a dominant trait. Dominant traits are never covered, so they can't skip generations.(4 votes)
- sorry for bothering but if both parents have freckles and there son/daughter dont have freckles would d that be possible if yes how please(2 votes)
- The only way the parents can have freckles and their offspring don't if that if both parents are heterozygous dominant. So Ff × Ff= FF,Ff,Ff, ff. That means one of their offspring won't have freckles.(6 votes)
- A horizontal line between a male and a female means?(2 votes)
- It means that they have had offspring- watch the first minute or so of the vid, that explains what everything on the chart is.(5 votes)
- How could the cross for the parents ( father x mother) be written using the dash technique for the unknown genes?(3 votes)
- Hmm, I think it would be something like this:
A_ x A_
A_ x AA
A_ x Aa
A_ x aa
where A: dominant, a: recessive, and the dash _ is the unknown allele(2 votes)
- How would you find the genotypes of the parents and offspring if the pedigree is about diseases? What if it's about male and female and the alleles are the superscripts? How would that situation work?(3 votes)
- [Instructor] What you see depicted here is known as a pedigree. And a pedigree is a way of analyzing the inheritance patterns of a trait within a family. And it can be useful to understand more about that trait, maybe to make some insights about the genetics of that trait, and it's a way to think about what's happened in the past in a family, and then maybe we can help get some probabilities or get some understanding of what might happen in the future. But let's just break it down, so we understand all of the different parts of a pedigree. So big picture, a circle represents a female in the family. And a square represents a male in the family. If either the circle or the square is colored in, like we see right over here, or we see right over here, that means that that person exhibits the trait. And the trait of this particular pedigree is for is the trait of freckles. And whether or not we're colored in, that is a phenotype. That is an observed trait. You just look at the person and say do they have freckles or not. This male right over here does not have freckles. This female right over here does have freckles. This male right over here does have freckles. But once again, this phenotype, that's the observed characteristic, we don't know exactly the genotype just from this. Although we might be able to infer some ideas about the genotype by seeing how the phenotype patterns spread from generation to generation. But just going back to understanding the pedigree itself. When you have a horizontal line connecting a male and a female, it's called a marriage line. And it means that they are coupling up and they are reproducing. They don't necessarily, I guess, have to be married. It's more that they reproduce. So this male and this female have reproduced. And then this vertical line that goes from that horizontal line, that's known as the line of descent. So it's going from that first generation to the second generation. And so all of the people connected to that vertical line at the bottom of the vertical line, these are their children. All the people who are directly connected to this. And this is known as a sibling line. So, this person, this person and that person, they are all brothers and sisters. You can see that generation one, they had two daughters, one of whom exhibited freckles, and one son, who had freckles. Now these other people in generation two, these aren't children of the first generation. These are people, you could say, who are brought into the family. They either married into the family, or you could just say they reproduced with the children. But that's what's happening with generation two. And so you can see, you have another what's known as a marriage line, but I guess it could be a coupling line, a line of descent, and then they have two daughters in this case. So it turns out that freckles is an autosomal dominant trait. And I will explain what that means in a second. Autosomal dominant, dominant trait. Autosomal means that it is a trait associated with one of the non-sex chromosomes. We have 23 pairs of chromosomes as humans. One of those pairs determines our sex, the other ones don't determine our sex. So this means that freckles is associated with one of the 22 pairs of chromosomes that do not determine your sex. And dominant means that in general you get two versions of a gene. One from your mom, and one from your father. And each of those versions of the gene for say whether or not you have freckles is known as an allele. And if a trait is autosomal dominant, that means that if you have even just one allele for that trait, that you are going to exhibit the trait. And so, for example, if the alleles for freckles, if capital F is you have freckles, it's dominant, so you write it in capital, and lowercase F means that you don't have freckles, if someone has a genotype of capital F, capital F, or capital F, lowercase F, or, I guess we could say lowercase F, capital F if we wanted to think about order. Which one you're getting from which parent. Well then in all of these situations, they would exhibit the phenotype of freckles. And we talk about genotype and phenotype in other videos. And of course, the only genotype in which they would not exhibit freckles would be having both of the recessive traits. So with this out of the way, what can we infer about the genotype of this individual right over here? And this individual will sometimes be referred to as individual I-2. They're in generation one, and they are individual two in generation one. Well, we know that they exhibit freckles. So we know for sure that since the phenotype is freckles, they're in one of these scenarios. And these two, these two are frankly equivalent. So this person, we know that they're either capital F, capital F, so that would be homozygous dominant. Or they're capital F, lowercase F. Which are, they are a heterozygote. Well, let's first think about the situation if they are homozygous dominant. If they are homozygous dominant, that means to every one of her children, she would give one of these alleles. And either of those are dominant. And so that would mean if this were the case, that all of her children would get at least on dominant allele. Well, if they all get at least one dominant allele, then all of her children would have freckles. But we're seeing a situation where all of her children do not have freckles. Two of her three children had freckles. So this cannot be the case. So this individual right over here must be heterozygous for freckles. So they must be capital F, lowercase F. And what do we know about this individual right over here, the person that she coupled up with? Well, they don't exhibit the phenotype for freckles. So they must be lowercase F, lowercase F. And then from that, you might be able to intuit a lot more about that. And we'll do that in future worked examples.